Cotton is the world's most widely used textile fiber. The popularity of cotton can be attributed, in part, to the relative ease of cotton production compared to other fibers and the applicability of cotton fiber to a wide variety of textile products. For example, the majority of fabrics used in the garment and home furnishings industries are manufactured from cotton fiber. One of the reasons that cotton is a widely used textile in the apparel industry is that it is very comfortable to wear. Cotton fabric is comfortable to wear because this fiber has relatively high level of moisture absorption and good wicking properties.
One disadvantage of cotton fabric, however, is that it ignites easily and burns rapidly. The flammability of a fabric is dependent upon its composition. Mehta, R. D., Textile Research Journal 44(10): 825-826 (1974), incorporated herein by reference, for example, found that the extent of flame and glow resistance of a fabric increased as the carboxyl and metal contents of the fabric increased. In view of the danger posed by flammable textiles in general, the government has promulgated consumer safety regulations for textiles including safety standards for carpets and rugs, mattresses and children's sleepwear. The flammability characteristics of textiles used to manufacture upholstery found in motor vehicles and airplanes are also regulated by the government.
In order to reduce the inherent flammability of cotton fabrics, cotton fiber can be combined with inherently flame resistant fibers, such as synthetic fibers. For apparel use modacrylic fibers and matrix fibers of vinal/vinyon, among others, have been used. The resulting fabrics frequently lack the performance properties and consumer appeal of pure cotton fabric. Fiber composed of 50% vinal and 50% vinyon, for example, is not strong enough to form its own fabric and is not easily dyed. Another disadvantage of this method of producing fire resistant fabric is that yarns containing two or more fibers with different flammability characteristics tend to produce fabrics having non-uniform cross-sectional areas, and therefore, non-uniform fire resistant characteristics.
Alternatively, cotton fabric can be treated with flame retardant chemicals that change or interrupt the burning process known as pyrolysis. Cotton fabric treated with flame retardant chemicals, however, typically lack the performance properties and consumer appeal of pure cotton fabric.
During pyrolysis textile materials must first undergo decomposition to form volatile combustibles before they will burn. Decomposition occurs when the textile material is exposed to a sufficient source of heat. The decomposition temperature for textile materials is dependent upon the composition of the material and is different for different fibers. When the textile material decomposes, volatile materials are formed. The volatile materials ignite in the presence of oxygen to produce heat. The heat produced during pyrolysis may cause further decomposition of the textile material leading to its complete destruction.
The application of flame recardant chemicals may interrupt pyrolysis. For example, the flame retardant may be converted upon heating into acids and bases that catalyze decomposition of the textile at lower temperatures than are required for the formation of volatile combustibles. Compounds containing phosphorus are converted to acidic materials that catalyze the thermal decomposition of the polymer. Alternatively, the flame retardant may decompose or sublime upon heating to release large amounts of nonflammable vapors which exclude oxygen from the flame.
A need exists for a natural cotton fiber that is inherently flame resistant such that fabric made from the fiber complies with flammability safety regulations without application of flame retardant chemicals, or with application of reduced amounts of flame retardant chemical compared to fabric made from known cotton fiber. In addition, a need exists for a naturally colored cotton fiber that is inherently flame resistant such that fabric made from the fiber does not have to be treated with chemical dyes and fire retardants. A need exists for cotton varieties that produce flame resistant fiber and breeding methods for selection of cotton varieties that produce fiber that is inherently flame resistant.